Automatic post mold curing apparatus for use in providing encapsulated semiconductor chips and method therefor

ABSTRACT

A post mold curing apparatus for use in association with a molding line system for providing plastic encapsulated semiconductor chips mounted on leadframes is disclosed which includes a leadframe carrier having a rotary, substantially cylindrical shaped assembly for containing and moving a plurality of semiconductor chips and their associated leadframe strips into both an elevated temperature post mold curing region and into a lower temperature cool-down region. Each of the leadframe strips with their associated semiconductor chips are sequentially inserted into cavity regions located in the cylindrical assembly to assist in moving each of the plurality of leadframe strips through the elevated temperature post mold curing region, and subsequently, each of the leadframe strips with their associated semiconductor chips are removed from the cavity regions after passing through the lower temperature cool-down region.

FIELD OF THE INVENTION

This invention relates generally to molding line systems for producingencapsulated semiconductor chips and, more specifically, to an automaticpost mold curing apparatus for use in this type of system and methodtherefor which provides a substantially cylindrical assembly which holdsand rotates a plurality of encapsulated semiconductor chips and theirassociated leadframe strips through both an elevated temperature postmold curing region and a low temperature cool-down region.

DESCRIPTION OF THE PRIOR ART

After having been encapsulated, semiconductor chips need to be cured atan heightened temperature for a substantial period of time. In the past,this part of the production of encapsulated semiconductor chips has beenaccomplished in a batch type manner. For instance, after a batch or agroup of semiconductor chips have been encapsulated by a relatively hot,plastic fluid, they are typically near 180 degrees Celsius. Afterallowing the batch of encapsulated semiconductor chips to cool down toroom temperature, the group of encapsulated semiconductor chips andtheir associated leadframe strips are loaded into an oven for curing atapproximately 150-160 degrees Celsius for 4-5 hours. After the group ofencapsulated semiconductor chips has been cured, they are again allowedto cool down to room temperature before they are moved to a dambarcutting/debris removing part of the production line. In review, from thecompletion of the molding operation to the commencement of the dambarcutting/debris removing operation, a group of leadframe strips and theirencapsulated semiconductor chips proceed from 180 degrees Celsius downto room temperature, up to 150-160 degrees Celsius, and back down toroom temperature over a period of at least 4-5 hours. Severaldisadvantages to this approach become evident upon realizing that itwould be significantly more time and energy efficient for the 180 degreeleadframe strips to be directly input to a curing oven since no time iswasted in waiting for the strips to reach room temperature and since theenergy required to raise the strips from room temperature to a curingtemperature of approximately 150-160 degrees Celsius is saved.Furthermore, the undesirable thermal stress placed upon the leadframestrips and their encapsulated semiconductor chips which is associatedwith cooling from 180 degrees Celsius to room temperature and thenheating up to 150-160 degrees Celsius is another avoidable aspect of theprior art approaches. In particular, by direct delivery of the 180degree leadframe strips from a molding apparatus to the 150-160 degreepost mold curing apparatus, unnecessary thermal stress is avoided. Inaddition, it would be advantageous to deliver the leadframe stripsautomatically, sequentially, and directly from a molding apparatus to apost mold curing apparatus, thereby eliminating unnecessary batchhandling of the leadframe strips and, consequently, reducing thelikelihood of product malfunctions since, in general, the number ofproduct errors tends to decrease as the amount of product handling isminimized. Therefore, a need existed to create an automatic post moldcuring apparatus for use in producing encapsulated semiconductor chipsthat saves time and energy while simultaneously reducing product defectsthat are attributed to excess thermal stress on and handling of theproducts.

SUMMARY OF THE INVENTION

In accordance with one embodiment of this invention, it is an object ofthis invention to provide an automatic post mold curing apparatus foruse in producing encapsulated semiconductor chips.

It is a further object of this invention to provide an automatic postmold curing apparatus that is an integral part of a continuous, in-linesystem for producing encapsulated semiconductor chips.

It is another object of this invention to provide an automatic post moldcuring apparatus that minimizes unnecessary heat-up and cool-downperiods associated with the production of encapsulated semiconductorchips, thereby minimizing thermal stress.

It is yet another object of this invention to provide an automatic postmold curing apparatus that minimizes needless handling of leadframestrips and their encapsulated semiconductor chips.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with one embodiment of this invention, an automaticmolding line system for packaging semiconductor chips is disclosedcomprising, in combination, wire bonding means for providing wire bondsbetween portions of each of the semiconductor chips to selected portionsof associated leadframe strips, plastic molding means coupled to thewire bonding means for encapsulating each of the semiconductor chips,.marking means coupled to the plastic molding means for marking aplastic housing for each of the semiconductor chips with anidentification designation, post mold curing means coupled to themarking means and having a substantially cylindrical shaped assembly andalso having a plurality of slots therein for holding the semiconductorchips and the associated leadframe strips and for rotating thesemiconductor chips and associated strips through at least a hightemperature region and a low temperature region to permit curing of theplastic housing, dambar cutting means coupled to the post mold curingmeans for removing dambars from the leadframe strips and for alsoremoving excess debris from the plastic housing of each one of thesemiconductor chips, plating means coupled to the dambar cutting meansfor plating selected portions of the leadframe strips, means locatedbetween the dambar cutting means and the plating means for off-loadingthe leadframe strips from the dambar cutting means and for subsequentlyon-loading the leadframe strips to the plating means, trim and formmeans coupled to the plating means for removing excess portions from theleadframe strips and for forming leads extending from the semiconductorchips, and means coupled to the trim and form means for moving each ofthe leadframe strips away from the trim and form means to permit use ofcompletely packaged semiconductor chips. This system also includes meansfor sequentially inputting the leadframe strips to the cylindricalshaped assembly of the post mold curing means and for sequentiallyoutputting the leadframe strips from the cylindrical shaped assembly ofthe post mold curing means after each of the leadframe strips completepassage through both the high temperature region and the low temperatureregion.

In accordance with another embodiment of this invention, a post moldcuring apparatus for use in association with a molding line system forproviding plastic encapsulated semiconductor chips mounted on leadframesis disclosed comprising, in combination, rotating leadframe carriermeans comprising a rotary, substantially cylindrical assembly forcontaining and moving a plurality of semiconductor chips and theirassociated leadframe strips into both an elevated temperature post moldcuring region and into a lower temperature cool-down region, and meansfor inserting the semiconductor chips with their associated leadframestrips into cavity regions located in the cylindrical assembly prior tomoving each of the plurality of leadframe strips through the elevatedtemperature post mold curing region and for removing the semiconductorchips with their associated leadframe strips from the cavity regionsafter passing through the lower temperature cool-down region.

In accordance with yet another embodiment of this invention, a method ofoperating a post mold curing apparatus for use in association with amolding line system for providing plastic encapsulated semiconductorchips mounted on leadframes is provided comprising the steps ofproviding rotating leadframe carrier means comprising a rotary,substantially cylindrical assembly for containing and moving a pluralityof semiconductor chips and their associated leadframe strips into bothan elevated temperature post mold curing region and into a lowertemperature cool-down region, and providing means for inserting thesemiconductor chips with their associated leadframe strips into cavityregions located in the cylindrical assembly prior to moving each of theplurality of leadframe strips through the elevated temperature post moldcuring region and for removing the semiconductor chips with theirassociated leadframe strips from the cavity regions after passingthrough the lower temperature cool-down region.

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following, more particular,description of the preferred embodiments of the invention, asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of the automatic molding linesystem for packaging semiconductor chips.

FIG. 2 is a simplified perspective view of the post mold curing andcool-down apparatus showing a leadframe strip with its encapsulatedsemiconductor chips being inserted into a slot in an elevatedtemperature post mold curing region and another leadframe strip with itsencapsulated semiconductor chips being removed from a slot in a lowtemperature cool-down region.

FIG. 3 is a front view of the post mold curing and cool-down apparatusof FIG. 2.

FIG. 4 is a cross sectional view of the post mold curing and cool-downapparatus taken along the line 4--4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an automatic molding line system for packagingsemiconductor chips is shown and is generally designated by referencenumber 10. A wire bonding portion 12 creates wire bonds between portionsof semiconductor chips and selected portions of associated leadframestrips. The output from the wire bonding portion 12 is coupled to aninput of a molding portion 14 of the system 10. The molding portion 14encapsulates semiconductor chips in plastic. The encapsulatedsemiconductor chips and their associated leadframe strips leaving themolding portion 14, enter a marking portion 16 where the plastic housingfor each semiconductor chip is marked with an identificationdesignation. The output from the marking portion 16 is coupled to a postmold curing and cool-down portion 18. Each one of the plurality ofencapsulated semiconductor chips and their associated leadframe stripsare sequentially loaded into their respective slot in a substantiallycylindrical shaped, rotating assembly of the post mold curing andcool-down portion 18. As the assembly rotates, each of the leadframestrips are moved through both a high temperature region for curing theencapsulated semiconductor chips and a low temperature region forcool-down. Following curing and cooling of the encapsulatedsemiconductor chips, a dambar cutting and debris removal portion 20removes dambars from the leadframe strips and dislodges excess debrisfrom the plastic housing of each of the semiconductor chips. A platingportion 24 plates selected portions of the leadframe strips while anoff-load/on-load portion 22 is coupled between the dambar cutting anddebris removal portion 20 and the plating portion 24. The output fromthe plating portion 24 is coupled to an input of a trim and form portion26 which removes excess portions from the leadframe strips and formsextended leads from the semiconductor chips. An OFF-LOAD portiondelivers each of the leadframe strips away from the trim and formportion 26 to permit use of completely packaged semiconductor chips.

Referring to FIG. 2, the post mold curing and cool-down portion 18 ofthe system 10 from FIG. 1 is displayed as the post mold curing andcool-down apparatus 18. A container 28 functions to enclose and insulateinterior portions of the post mold curing and cool-down apparatus 18.Note that the container 28 is provided with at least an input and anoutput opening to allow the input and the output of each of theleadframe strips 36 with their associated encapsulated semiconductorchips. A rotary, substantially cylindrical shaped assembly 30 has aplurality of slots 34 for holding and moving each of the leadframestrips 36 through both a HEATING or an elevated temperature post moldcuring region and a COOL-DOWN or a lower temperature cool-down region asthe assembly 30 rotates. A shaft 32 transfers a rotational driving forceto the assembly 30 from a drive source which is not shown for the sakeof simplicity.

Referring to FIG. 3, a front view of the post mold curing and cool-downapparatus 18 shows only a portion of the slots 34 of the assembly 30.Typically, a larger portion of the circumferential area of the assembly30 is dedicated to the HEAT application than to the COOL applicationsince, in general, curing of encapsulated semiconductor chips usuallyrequires 4-5 hours while cooling demands less time.

Referring to FIG. 4, this view of the post mold curing and cool-downapparatus 18 shows the relative positioning between the input positionand the output position for the leadframe strips 36.

OPERATION

Each of the encapsulated semiconductor chips and their associatedleadframe strips 36 are sequentially input to one of the slots 34 in theassembly 30. Focusing on a single one of these leadframe strips 36, itrotates through the HEATING region of the post mold curing and cool-downapparatus 18 for a typical period and temperature of 4-5 hours at a150-160 degrees Celsius. After having been cured, the leadframe strip 36passes through the COOLING region to bring the temperature of theleadframe strip 36 to approximately room temperature upon exitingthrough the output slot of the post mold curing and cool-down apparatus18. Note that as one leadframe strip 36 enters the assembly 30, anotherleadframe strip 36 exits so that a sequential rather than a batchhandling of the leadframe strips 36 is accomplished.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention. For example, the heating and/or cooling timesand temperatures could be changed if desired. Also, if desired, onecould insert leadframe strips 36 into every other slot 34, or perhaps atsome other spacing interval, as opposed to filling every slot 34.

I claim:
 1. A post mold curing apparatus for use in association with amolding line system for providing plastic encapsulated semiconductorchips mounted on leadframes comprising, in combination:rotatingleadframe carrier means comprising a rotary, substantially cylindricalassembly for containing and moving a plurality of semiconductor chipsand their associated leadframe strips into both an elevated temperaturepost mold curing region and into a lower temperature cool-down region;and means for inserting said semiconductor chips with their associatedleadframe strips into cavity regions located in said cylindricalassembly prior to moving each of said plurality of leadframe stripsthrough said elevated temperature post mold curing region and forremoving said semiconductor chips with their associated leadframe stripsfrom said cavity regions after passing through said lower temperaturecool-down region.
 2. The apparatus of claim 1 wherein said semiconductorchips are integrated circuit chips.
 3. The apparatus of claim 1 whereinsaid cavity regions comprising a plurality of slots with each one ofsaid slots accommodating each one of said plurality of semiconductorchips and their associated leadframe strips.
 4. The apparatus of claim 3wherein each one of said plurality of slots being configured to retainleadframe strips of dissimilar dimensions.
 5. The apparatus of claim 1wherein said elevated temperature region is at an elevated temperaturebelow a molding temperature used to form a plastic encapsulation of saidsemiconductor chips with their associated leadframe strips.
 6. Theapparatus of claim 1 wherein said lower temperature cool-down region issubstantially equivalent to room temperature.
 7. The apparatus of claim1 wherein said means for inserting incrementally inserts each one ofsaid plurality of leadframe strips one at a time into one of said cavityregions of said rotary, cylindrical assembly.
 8. The apparatus of claim1 wherein said means for removing incrementally ejects each one of saidplurality of leadframe strips one at a time from one of said cavityregions of said rotary cylindrical assembly.